Drivers and other users of cars appreciate the convenience of doors which unlock when they arrive, and lock again when they go away—and the same holds for anything which should be available for authorized users, and locked for anyone else. The instant invention is directed to improvements in locking and unlocking, especially in the context of a car. This can improve security over existing systems.
A simple remote lock and unlock system may use a key fob with buttons for a user to unlock and lock e.g. a car. Such a system has the disadvantage that the user must push the unlock button when the key fob is within signalling range of the car, meaning that the user must typically have one hand free to press the button. Likewise, when leaving the car, the user must have a hand free to lock the door—and must also remember to operate the lock.
An alternative system, often called “keyless” because there is no need to take a key fob in the hand, uses a key fob which continuously or regularly broadcasts a signal. When the car detects the signal in its proximity, it unlocks the door. When the signal is no longer in proximity, the car locks the door again.
Keyless locking and unlocking is an improvement over buttons, because the user no longer needs a hand free to operate the lock; proximity of the key fob is enough to unlock and lock the car.
The idea is that the key opens the car only when it is in physical proximity to the car. However, it has proven possible to “fool” a car into believing the key is in proximity by using a radio relay. The relay consists of transcievers, which transmit the weak signals exchanged between a key fob and a car over long distances, typically using a different radio system. The car detects the presence of the key and performs a verification, for example a challenge/response. If the key answers correctly, the car assumes that the key is nearby, and unlocks. The car assumes that a successful exchange with the key imies that the key is in proximity, because the radio system used does not work over long distances. The car may use alternate approaches to testing the physical proximity, such as a GPS assist for bot car and key fob, or by measuring the time of transmission. However, these alternatives may not be secure or precise enough.
The instant invention offers an alternative improvement wherein, in some embodiments, a time or time window is created within which the car accepts a request rom the key fob to unlock as being a valid request from a key in proximity. The time window may be an instant when the key fob gets a signal from the user—e.g. a key press—or it may be a limited amount of time during which the key signals to the car that the car should unlock when it determines that the key is in proximity. In one embodiment, the key fob may transmit two different signals, namely one signal as an unlock signal to unlock the car, and the other as an identification signal which, when it disappears, is taken as a signal to lock the car. In this way the key fob establishes a time or time window when the car will respond to proximity of the key by unlocking the car. A relay attack can thus only work in the time between when the user signals that the car should unlock, and the time when the car does unlock.